Storm ready

A luxury apartment block needed a unique drainage solution

A brand new luxury apartment complex in London’s Kensington has been fitted with two EcoBloc Flex stormwater tanks from Graf UK – providing a highly effective drainage system that reduces the loading on the public sewers and complies fully with official runoff requirements set by the local authority and Thames Water.

Set in an area of landscaped gardens that stretch from the south side of Holland Park to Kensington High Street, the Hollandgreen development includes three residential blocks, comprising 54 apartments. Developed by real estate company Chelsfield, the apartments share the development land with the new Design Museum site (formerly home to the Commonwealth Institute) – a Grade II-listed building boasting the largest parabolic copper roof in the world.

Given the museum roof’s undulating design, rainwater collects at two focused locations, so a siphonic drainage system is in place to discharge this water instantaneously and avoid buildup on the roof. Flow rates into the siphonic outlets can be as high as 180l/s – and to meet criteria set by the Royal Borough of Kensington and Chelsea, the flow rate of surface water being discharged from the new development and the Design Museum roof to the public sewer network must stay within strict lower limits. As part of its overall engineering remit, consultancy Arup was tasked with finding a safe, sustainable stormwater management solution for Hollandgreen.

Arup’s public health team (led by Dan Costelloe) specified two bespoke EcoBloc Flex tanks from Graf UK. Mike Carter, project director for Arup, explains: “The parabolic roof of the Design Museum at Hollandgreen presented a unique drainage challenge for Chelsfield. Our task was to find a solution that would not only limit the discharge to the public sewer to 30 per cent of the instantaneous run-off rate – and manage excess stormwater safely and effectively – but would also fit with the design and layout of the luxury development. Together with the team at Graf UK, we were able to design a completely tailormade system to do just that. Made up of two individual EcoBloc Flex tanks, it meets the project’s exact size and shape requirements.

“As the ground we were working with was clay-heavy (typical of London), we specified attenuation tanks (rather than infiltration) – allowing for ultimate control of water release back into the sewage system. What’s more, Chelsfield was originally informed the site would need up to a system of 315m3 – but thanks to the detailed analysis we carried out with Graf UK, combined with the use of compact, space-maximising EcoBloc Flex tanks, we were able to fulfill requirements with a reduced storage capacity of just 212m3. This resulted in significant financial savings and overall instantaneous discharge reduced to 70l/second.”

EcoBloc Flex can be made to any shape or size and can be positioned as shallow or as deep underground as required, without taking up valuable surface areas. It has a heavy-duty lorry bearing capacity of 60 tonnes – a must for the Hollandgreen development, as one of the main EcoBlocstorage tanks is located on the direct approach to the Design Museum loading bay. Even under extreme loads, it boasts a storage coefficient of 96 per cent. EcoBloc Flex tanks are also designed with straightforward maintenance in mind, with Vario shafts and inbuilt inspection channels providing easy access for advanced camera technology. These cameras are used to periodically check for any silt or gravel build-up – ensuring optimum performance for thelifetime of the system.

Mike continues: “As well as ultimate ease and speed of installation, EcoBloc Flex offered us a hassle-free future maintenance solution – making it ideal for this forward-thinking development. Its flexible, modular design also meant we were able to make it fit seamlessly with the existing drainage network by positioning it exactly where we needed it: lower than the water flow, but higher than the outlets into the sewers. The Graf UK team was similarly flexible – working closely with our design team to make sure the system ticked all the boxes, while keeping within the project’s tight timeframes.”

Hollandgreen’s water systems have been designed to Code for Sustainable Homes Level Four standards, and also feature grey water re-use for irrigation, WC flushing and façade cleaning. In addition to the apartments and the Design Museum, the complex also includes a luxury spa with swimming pool, a fitness centre, studio space and treatment rooms, and an entertainment area including a cinema, golf simulator and children’s playroom.

Graf UK’s national specification manager, Kevin Reed, adds: “We’re delighted to have had such an important part to play in this exciting and innovative project. Hollandgreen’s new, custom-designed stormwater attenuation system showcases the true versatility of our EcoBloc Flex modules – and is a perfect example of how they can be used to overcome a whole host of drainage challenges. With extreme weather and flooding becoming increasingly commonplace in the UK, demand for sustainable urban drainage systems (SuDs) is steadily on the rise. At Graf UK, we’re proud to offer cutting-edge solutions that not only meet this demand now, but are also fit for the future – designed with simple, ongoing maintenance and quality, longterm performance in mind.”

Graf UK Ltd (a subsidiary of Germanbased Otto Graf GmbH) is a European market leader in the water management sector. The company provides innovatively designed rainwater harvesting, stormwater and wastewater management systems that are manufactured in Germany at one of the world’s most modern and sustainable production facilities.

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